(1) Technical Field
The present invention relates to a wafer cassette which holds a plurality of semiconductor substrates and more particularly to a cassette for containing and supporting a plurality of thin substrates such as semiconductor wafers and for storing and handling the fragile wafers, each of which are loaded and unloaded numerous times during the forming of integrated circuits therein.
(2) Description of the Prior Art
A cassette has been conventionally used for storing and supporting a plurality of fragile semiconductor substrates. The stored substrates, each of which are loaded and unloaded many times during the manufacturing process, both manually and automatically, are susceptible to damage. Cassettes are typically molded as a one-piece container is described with reference to FIGS. 1, 2 and 3, of the prior art. The cassette 120 is made in the form of an open container having only four sides with a wide opening at the top for inserting and removing substrates, and a narrower opening, relative to the outside dimensions of a substrate at the bottom of the cassette. This allows maximum exposure to process fluids while securely containing each substrate. The four sides include two side panels 121, 122 and two end panels 123, 124. Each side panel has a straight upper portion and a curved lower portion with grooves that have an elongated V shaped cross-section 125 formed within its interior surfaces. Each curved portion converges inward forming the narrower opening for the bottom; this is best illustrated in FIG. 1. In this conventional cassette 120 having the aforementioned configuration, a plurality of substrates 10 are contained in parallel with each other while guided and retained in the elongated V grooves 125.
The substrates are usually loaded or unloaded when the cassette is in a vertical position as shown in FIG. 3 illustrating a cross-sectional side view of a cassette 120 showing a common problem of the substrates 10 protruding out beyond the front opening 130 of the cassette. When the cassette is placed in a vertical position, any vibration that may be caused by a myriad of disturbances can easily cause substrates to slide out from inside the cassette to a position of exposure to damage by interfering with substrate handling hardware. This has always been a problem with conventional cassettes when handling fragile substrates. During automatic handling of substrates, by robots and the like, the fragile substrates are vulnerable to breakage during insertion or removal because of this protrusion problem.